Loss of Monoethylene Glycol to CO2- and H2S-Rich Fluids: Modeled Using Soave–Redlich–Kwong with the Huron and Vidal Mixing Rule and Cubic-Plus-Association Equations of State

Abstract

Produced reservoir fluids often carry formation water, and gas hydrates may form in pipelines transporting the produced fluid, unless an inhibitor is added. Monoethylene glycol (MEG) is one of the most widely used hydrate inhibitors, because loss to the gas phase is typically low. The loss of MEG to CO2-rich fluids can, however, be quite significant and must be accounted for in design and economical evaluations. Accurate thermodynamic models are needed to predict the inhibition effect as well as the loss of the hydrate inhibitor to the non-aqueous phases. In this work, the Soave–Redlich–Kwong (SRK) equation of state with the Huron and Vidal (HV) mixing rule and the cubic-plus-association (CPA) model have been compared for mixtures of gas, H2O, and MEG. The models have been tested on phase equilibrium data for binary mixtures of gases (e.g., C1, CO2, and H2S) and polar components (H2O and MEG) as well as on hydrate inhibition data. Overall, the SRK–HV and CPA models provide similar results, but an exception is gas mixtures rich in CO2, for which notable differences are seen for the MEG concentration in the gas phase.